Projects
Ceramic wall clocks
A clock is the one pottery project where a piece of hardware has to fit your pot, and your pot is going to shrink by roughly a tenth before the hardware ever sees it. Almost everything that goes wrong with a handmade clock comes out of that one sentence. Get the hole, the thickness and the hand length right and the rest of it is just a good flat pot with a drawing on it.
The short version
All of it, in six lines
- Buy the movement before you make the clock. Get one rated for a dial up to half an inch thick. Anything shorter will not reach through fired stoneware, and a shaft that is too short cannot be fixed.
- Cut the center hole at half an inch, wet. Our clay shrinks between ten and thirteen percent, so half an inch lands somewhere near seven sixteenths after the glaze firing. That clears the standard shaft with room for glaze.
- Dish it, do not flatten it. A shallow curve from a slump mold is far stiffer than a flat disc, and the curve gives the movement somewhere to sit.
- Dry it slowly, flat, between two boards. Warping is the thing that actually ruins clocks, and it does its work while you are not in the building.
- Carve the keyhole into the thickness, not onto the back. Anything glued or stuck on the back stops the piece sitting flat, on the kiln shelf and on the wall.
- Buy the hands after it is fired. The clay shrinks, the hands do not, so measure the real thing. Under five inches for a standard movement.
The one number to remember
Half an inch, wet, for the hole. Every other measurement on this page can be fudged later. That one cannot, because you cannot make a fired hole bigger with anything you have at home.
How to use this page
Why there is a video and a list for the same thing
Watching somebody make something tells you things writing cannot. How firm the clay is when they pick it up. How gently they set a slab down. How long they wait before doing the next thing. Six seconds of video carries what six paragraphs cannot.
Reading does the other half of the job. It gives you the order, the numbers, and the reason a step exists, and it holds still on a screen while your hands are covered in clay. Nobody has ever scrubbed back through a seventeen minute video with a wet thumb to find the bit about hole size.
The two together stick better than either one alone. Watching gives you the picture. Having it written down in steps gives you something to rehearse against and check yourself on, which is most of what turns a thing you saw into a thing you can do.
So this page is built to be used twice. Watch a clip all the way through before you touch anything. Then keep the short lists open on your phone at the table. Every list here is deliberately short enough to hold in your head between glances, and there is a copy button further down that drops the whole thing into your notes app.
There is a shorter version of this page
The toggle at the top switches between everything we know and the working version you can act on tonight. Your choice follows you to every other guide on this site, so you only have to pick once.
Start here
A clock is a plate that has to fit a machine
Everything below is one cross section. If you understand where the movement sits and why the back needs a rim, the rest of this project is ordinary slab work.
Every other pot you make in this building only has to satisfy you. A clock has to satisfy a five sixteenths of an inch metal shaft that was manufactured to a tolerance, by a company that has never heard of shrinkage. That is the whole difficulty, and it is also why a clock is such a satisfying thing to get right.
- The face, seen edge on Shallow and dished, not dead flat. A curve is stiffer.
- The hole Cut at half an inch wet. Finishes near seven sixteenths.
- The movement A plastic box that lives in the hollow behind the face.
- The shaft, washer and nut Comes through from the back. Must be longer than your clay is thick.
- The hands Bought after firing, sized to the fired clock.
- The back rim Stands proud of the movement so the clock sits flat.
- The keyhole Cut into the rim, not stuck onto it.
Some numbers to hang on that drawing. The movement is close to standardized at roughly two and an eighth inches square and five eighths of an inch deep, running on one AA battery, with a threaded post five sixteenths of an inch across. The hands want to be under five inches for a standard motor. The back rim wants to be at least three quarters of an inch tall once fired, which is what gives the box somewhere to live and the clock something flat to rest against the wall on.
Four numbers decide whether it works
Half an inch
The hole, cut wet. Big enough to survive shrinkage and glaze, small enough that the washer still covers it.
Half an inch
The dial thickness your movement must be rated for. Fired stoneware at a third of an inch defeats most craft store movements.
Five inches
The longest minute hand a standard movement will drive. Past that the motor stalls and you need a high torque one.
Twelve inches
A comfortable finished diameter. It keeps the hands under five inches and the weight under about four pounds.
Buy this first
The movement is not an afterthought
More handmade clocks are ruined at the checkout than at the wheel. Buy the mechanism before you cut a single circle and put it on the table next to you while you work.
More handmade clocks are ruined at the checkout than at the wheel. People make a beautiful piece, fire it twice, and then discover the ten dollar mechanism they grabbed has a shaft that stops a quarter of an inch short of the front of their pot. There is no fixing that. Buy the movement before you cut a single circle, and put it on the table next to you while you work.
The thing you want is a mini quartz movement. They are close to standardized: about two and an eighth inches square, five eighths of an inch deep, one AA battery, and a threaded shaft five sixteenths of an inch across. What varies between them, and the only thing you have to choose correctly, is how long that shaft is.
One question at the checkout
Does the listing say it fits a dial at least half an inch thick? If it does not say, buy from one that does. The second question only matters if your clock is bigger than about twelve inches: hands over five inches need a high torque movement.
Shaft length
Sold by the dial thickness it will clear: an eighth, a quarter, a half, five eighths, three quarters. Buy the half inch or bigger. Too long can be padded out with washers. Too short is scrap.
Torque
A standard movement drives hands up to about five inches. Longer than that and you want a high torque version, which handles hands up to about seventeen inches for a few dollars more.
Tick or sweep
A stepping movement ticks once a second. A continuous sweep movement is silent and costs a little more. In a bedroom, buy the silent one. You will not regret it and you might regret the other.
Hands
Usually a free choice with the movement, and usually the thing people pick too early. Wait until the piece is fired, measure the real thing, then order.
The hardware bag
A rubber washer, a brass washer, a hex nut, a small cap nut and often a hanger. Do not throw the rubber one away. On a slightly oversized ceramic hole it is what stops the movement wandering off center.
Where to get one
Craft stores carry them, and so does every clock parts supplier online. The listing always states the dial thickness. If it does not state it, buy from a listing that does.
Why the craft store default fails on pottery
Most cheap movements are built for a card, canvas or thin plywood dial, so their threaded post clears an eighth or a quarter of an inch. A stoneware clock face rolled at three eighths of an inch comes out of the kiln at about a third of an inch, which is already past a quarter inch movement before you add the washer and the nut. The half inch rating costs the same and removes the whole problem.
The part you cannot redo
The hole in the middle
Half an inch, wet. Never past five eighths.
Under half an inch and shrinkage can close it down onto the shaft. Past five eighths and the brass washer stops covering the hole, so you get a ring of daylight around your own hardware.
A wet hole shrinks by the same fraction as the pot around it, and our clay bodies shrink between ten and thirteen percent. So half an inch wet finishes near seven sixteenths on every clay we stock, which clears the standard five sixteenths shaft with room for a drip of glaze. Generous beats exact, because a fired hole cannot be made bigger with anything you have at home.
A wet hole shrinks by exactly the same fraction as the pot around it. Our clay bodies publish their shrinkage, and they run from ten to thirteen percent from wet clay to a finished cone 5½ piece. So a half inch hole cut in soft clay arrives at the far end somewhere between about seven sixteenths and a shade under it, which clears the five sixteenths shaft on every standard movement with enough room left over that a drip of glaze cannot close it.
The reason to be generous rather than exact is that a hole is easy to make bigger while the clay is soft and effectively impossible to make bigger once it has been fired to cone 5½. Fired stoneware is a ceramic material. Opening it up means a diamond core bit and running water, and even then you are drilling a hole in something you already love.
| Clay body | Published shrinkage | A ½″ wet hole finishes near | Clearance on a 5/16″ shaft |
|---|---|---|---|
| 52 Buff | 10% | 0.45″ | Roughly 0.14″ |
| B-Mix w/Grog | 11% | 0.45″ | Roughly 0.14″ |
| B-Mix | 12% | 0.44″ | Roughly 0.13″ |
| B-Mix w/Specks | 12% | 0.44″ | Roughly 0.13″ |
| Speckled Buff | 12% | 0.44″ | Roughly 0.13″ |
| Half & Half | 12% | 0.44″ | Roughly 0.13″ |
| #16 Porcelain | 13% | 0.43″ | Roughly 0.12″ |
Shrinkage figures are the ones published on each clay’s own product page, and they carry a couple of points of tolerance either way. Berlin Gray quotes its drying and firing shrinkage separately and lands in the same range.
Cutting it
- Find the real center first. On a wheel thrown face it is already there. On a slab, fold a paper circle of the same size into quarters and the crossing point is your center. Mark it with a pin, not a thumb.
- Cut while the clay is soft. Wet or barely firm. A half inch hole cutter, a piece of half inch copper pipe, or a small round cutter all work. Push straight down and twist rather than dragging.
- Clean both sides of the burr. The back edge is the one people forget, and it is the side the rubber washer has to seat against.
- Check it again at bone dry. Run the shaft of your movement through it. This is your last cheap opportunity to open it up, with a round file or a rolled piece of sandpaper, before the piece is a ceramic.
- Keep glaze out of it. Wax the hole, or wipe it clean with a damp sponge before the piece goes to the kiln. Glaze inside the hole shrinks it and can leave a sharp lip that eats the rubber washer.
The face
Three ways to make it, and what each one costs you
All three end in the same place: a round, even, faintly dished piece of clay with a hole in the middle. They differ in how much the clay fights you afterward.
Slab into a slump mold
Roll a slab, lay it into a shallow round slab mold, let it take the curve. Our first recommendation for a first clock.
- Roll at three eighths of an inch. Thinner warps and cracks, thicker gets heavy and starts fighting your movement’s shaft.
- Compress both faces with a rib before you do anything else. Rolling stretches the clay and compressing is how you take that stress back out.
- Slump, do not drape. A slump mold leaves the face gently concave, so the hands sweep over a surface that falls away from them. A drape mold gives you a dome, and the tip of a minute hand will foul it.
- Leave it in the slab mold until it is firmly leather hard. Lifting a slab out early is the single biggest cause of a warped piece.
- Cut the hole after it has taken the curve, not before, or you will distort it on the way in.
- Why the curve matters: a flat sheet of anything is easy to bend and a curved one is not. The same gentle dish that makes it look considered is also what keeps it from potato chipping in the kiln.
- The hollow behind the curve is where the movement goes, which is a second free win from the same decision.
- A shallow slab mold is better than a deep one. You want the look of a plate, not a bowl.
- The slab molds guide covers which ones we have, how they behave, and how to get a clean release.
A flat slab, no slab mold
Roll it, cut a circle, dry it dead flat. The simplest route and the least forgiving one.
- Roll at three eighths, compress both sides, and cut the circle around a template once the slab has firmed slightly. Cutting a soggy slab drags the edge oval.
- Dry it between two flat boards with a light weight on top. Not a heavy one: the piece has to be able to shrink underneath, and a heavy board drags it.
- Flip it once a day. The side facing up dries faster, and the piece curls toward whichever side dried first.
- Accept that a flat back means the movement stands five eighths of an inch proud behind it, so you will need to deal with that when you hang it.
- Best for small clocks, under about eight inches, where the span is short enough that warping has little leverage.
- Also the right choice if the design is a shape rather than a disc. A sun, a moon, a scalloped flower, an animal. Those read better flat.
- If you are cutting an outline shape, keep the material around the hole generous. The center is the one place that carries a load.
Thrown on the wheel
A very wide, very shallow plate. Harder to make, and the center is perfect without you having to find it.
- Throw it like a shallow plate on a bat, with a foot ring trimmed generously. That foot is the standoff and the firing support in one.
- Compress the floor hard and repeatedly. A thrown flat form that was not compressed will crack across the middle while it dries, and a clock is nothing but middle.
- Leave the floor thicker than you would on a plate. You are going to cut a hole through it and hang three or four pounds of stoneware on a screw.
- Cut the center hole at leather hard, on the wheel, so it is genuinely centered.
- Dry it slowly and upside down on its rim for the first day, then the right way up. Rims dry faster than floors and this evens it out.
- You can trim a keyhole slot into the foot ring while it is still on the wheel, which is the tidiest version of the hanging problem anybody has solved.
- Compressing the floor and the rim has its own guide, and it is the skill this method lives on.
The thing that actually ruins them
Flat is not free
Nobody loses a clock to a bad drawing. They lose it because a twelve inch disc spent four days on a shelf becoming a potato chip while nobody was in the room.
Nobody loses a clock to a bad drawing. They lose it because a twelve inch disc of clay spent four days on a shelf deciding to become a potato chip, and by the time anybody noticed it was bone dry and permanent. Warping is a drying problem and a handling problem, and both of them happen when you are not in the room.
- Compress both faces with a rib the moment you finish rolling. Rolling puts the sheet under tension and this takes it back out.
- Flip it once a day until it is firm. Whichever side dries first is the side it curls toward.
- Move it on a board, not in your hands. Every lift adds stress to a piece that is already fighting itself.
- Tent it loosely in plastic for the first few days, then between two boards with a light weight. A clock that took a week to dry is a clock that is still flat.
Clay remembers being stretched
Rolling a slab drags the particles into alignment and puts the whole sheet under tension. As the water leaves, it tries to go back. Compressing both faces firmly with a rib right after rolling is how you take that argument out of it early, and it is thirty seconds of work.
Whichever side dries first wins
A slab sitting on a board dries from the top. The top shrinks while the bottom is still full of water, and the edges lift. Flipping the piece once a day until it is firm costs you nothing and solves most of it.
Handle it as little as possible
Every lift, twist and slide puts new stress into a piece that is already under tension. Move it on a board rather than in your hands. If you must pick it up, use both flat palms and splayed fingers, and do it once.
Slow is the whole trick
Loosely tent it in plastic for the first few days so the whole piece loses water at one rate. Then between two boards with a light weight on top, then uncovered. A clock that took a week to dry is a clock that is still flat.
A weight, not a press
The board on top is there to discourage curling, not to hold the piece prisoner. It has to shrink underneath, and a heavy weight drags the clay against the board and produces cracks instead of curls. A second drywall board, or a piece of plywood, is about right.
And then the kiln gets a turn
- Fire it flat on a flat shelf. A large flat form that is only supported around its edge can sag in the middle at cone 5½. If your piece has a foot ring, it is strong enough to fire on it. If it is a plain flat disc, lay it straight down on the shelf and glaze the front only.
- Never fire a clock on stilts. Three points under a wide flat piece is how you get a wide flat piece with three dents and a wave in it.
- A warped bisque is a warped clock. Nothing in the glaze firing will flatten it back out. Check the piece against a straight edge before it goes in for glaze, and if it rocks, decide then whether you want to spend a glaze fee on it.
- Bisque firings are free here, so drying slowly and firing carefully costs you time and nothing else.
Geometry, briefly
The twelve marks
Set a compass to the radius and step it around the edge
It lands back where it started after exactly six steps, every time, on every circle. Halve each of those six gaps and you have twelve. No protractor, no ruler, no arithmetic, and it is exact rather than nearly right.
Twelve marks sounds like the fussy part and it is the easy part. Step the dividers around, bisect the six gaps you get, and you are done. Nothing on the face shrinks out of position, because it all shrinks together.
Twelve marks around a circle sounds like the fussy part and it is actually the easy part, because a circle is unusually cooperative about being divided into six. The radius of any circle steps around its own circumference precisely six times. That is not a rule of thumb, it is what a regular hexagon is, and it means a pair of dividers set to the radius of your clock will walk out twelve, two, four, six, eight and ten for you without measuring anything.
Then bisect each of those arcs by eye or with the same dividers and you have the odd hours. Somebody with a steady hand can do the whole thing in about ninety seconds on leather hard clay, and it is more accurate than anything you will manage with a ruler on a curved surface.
The alternative, if geometry is not your idea of a good evening, is to print a clock face at your finished size, prick through the twelve positions with a needle tool, and lift the paper. Both work. The compass method is faster once you have done it twice.
One thing you do not have to worry about: shrinkage. Everything on the face shrinks by the same fraction at the same time, so your marks stay exactly where you put them relative to each other and to the hole. The only part of this project that does not shrink is the pair of hands, which is why you buy those last.
Making the marks: stamp them, carve them, scratch them back through underglaze, sprig them on, or leave them out entirely. Twelve, three, six and nine is a perfectly readable clock and it is much harder to get wrong than freehand numerals.
Ways to actually make the marks
Stamped or impressed
Press a shape into leather hard clay at each position. Simple, fast, and glaze pools in the impressions and darkens them, so the marks read from across a room without any color at all.
Carved or sgraffito
Cut numerals or bars into the surface, or paint the face and scratch back through. Sgraffito gives you the crispest numerals available in clay and needs no drawing ability at all.
Painted in underglaze
The most direct route, and the one where a wobbly hand shows most. Sketch in pencil first, which burns away completely in the bisque, and use a liner brush rather than the one you glaze with.
Sprigged on
Small relief shapes pressed from a sprig mold and attached at each hour. Twelve identical marks with no chance of the twelfth drifting off style from the first.
Inlaid, or mishima
Carve the numerals, flood color into the grooves, scrape it back level. Fine, precise and permanent, and it survives a thick glaze better than a painted line.
Nothing at all
Twelve, three, six and nine, or four marks, or none. A clock face with no numbers is entirely readable and it is much harder to get wrong. Consider it seriously before you commit to freehand Roman numerals.
Leave room for the hands to live
The hour hand sweeps a small circle near the middle and the minute hand sweeps a big one. Anything in the band between those two radii is going to spend most of its life underneath a piece of metal. Put the detail in the center, out at the rim, or in the marks themselves, and keep the middle ring relatively quiet.
The finish
Glazing a clock
Front only
The back faces a wall for the rest of its life. Leaving it bare means the piece can lie flat on a kiln shelf, sits flat against plaster, and costs you nothing in appearance.
A clock face is a large, flat, vertical surface that somebody is going to look at from six feet away every single day, which is a harder test than a mug gets. Flat surfaces show everything: brush direction, thin patches, a run that started and stopped, the place where your hand changed grip. It is worth more care than the size of the piece suggests.
Dipping gives the most even coat and is awkward on something this wide, so most clocks get poured or brushed. If you brush, cross your directions between coats and keep each coat genuinely thin. If you pour, do it over a tub with the piece on a rack and get it done in one movement rather than several.
Any color you painted on before the bisque, underglaze, engobe or slip, goes on raw clay and gets fired once before a glaze touches it. Unfired color lifts straight off into a shared dipping bucket, and one piece is enough to spoil one.
- Keep glaze out of the hole and off the back. Wax both, or wipe them clean. A glazed back will not sit flat and a glazed hole will not fit your shaft.
- Gloss shows texture, matte hides it. If you stamped or carved the marks and are relying on glaze pooling to make them read, a matte will quietly flatten the whole effect. Ask at the glaze wall which of ours break over texture.
- Watch out for runny glazes on a piece fired flat. Lying on a shelf, a runny glaze does not run down, it spreads out toward the rim and off the edge. Keep it well back from the edge and put anything you are unsure about on a kiln cookie.
- Test tiles earn their keep here. A three hour piece deserves better than a jar lid as a preview, particularly if there is texture involved.
- Firing is charged by size, at five cents per cubic inch with a four dollar eighty minimum on the glaze firing. Measure the widest points. A twelve inch clock is a cheap thing to fire and an expensive thing to remake.
The last problem
Hanging three pounds of stoneware on a wall
A twelve inch clock weighs around three and a half pounds, and the movement stands five eighths of an inch proud behind it. Plan the hanging while the clay is soft, because every good answer has to be built in rather than added on.
A twelve inch clock a third of an inch thick weighs somewhere around three and a half pounds. That is heavier than every mass produced clock you have ever hung, and it is far more than the little plastic hanger in the movement’s hardware bag was designed for. Plan the hanging while the clay is still soft, because every good answer has to be built in rather than added on.
The two problems, and they fight each other
The movement stands five eighths of an inch proud
That box has to go somewhere, and on a flat backed clock it goes behind the middle. Hang that from a single point at the top and the piece pivots on the box and leans out at the bottom. It looks exactly as wrong as it sounds.
Anything stuck on the back stops it firing flat
A clay tab, a pocket or a loop added to the back lifts the piece off the kiln shelf and gives it three unsupported feet to sag between. The obvious fix for the first problem creates a second one.
The answer both times is the same: build the depth into the form
Give the piece a raised back rim, or a proper thrown foot ring, at least three quarters of an inch tall once fired. That gives the movement a hollow to sit in, gives the clock something flat to rest against the wall on, and gives you a solid band of clay to cut a keyhole into. The piece fires standing on that same rim, which it is easily strong enough to do. One decision, three problems gone.
Cutting the keyhole
- Cut it into the thickness, never onto the surface. A keyhole carved into a rim or a thickened boss leaves the back flat. A tab stuck on top of the back does not.
- Put it at the top, on the center line. Measure from the hole, not from the edge, because your rim is handmade and your center is not.
- Make it a keyhole, not a round hole. A wide opening at the bottom for the screw head to pass through, narrowing to a slot above it that the shank drops into. Roughly half an inch wide at the bottom and a quarter at the top, wet.
- Undercut the slot slightly so the screw head sits behind the clay rather than against it. A quarter of an inch of depth is plenty.
- Cut it at leather hard and clean it at bone dry. Same discipline as the center hole, and for the same reason.
If you forgot, and it is already fired
A metal sawtooth or D ring hanger will bond to fired stoneware with a two part epoxy, which is on our helpful items list for kintsugi work anyway. Scuff the spot with a wet diamond pad first so the epoxy has something to grip. It is a genuinely durable fix, it just is not as nice as one you planned.
On the wall itself
Three or four pounds wants a screw into a stud or a proper drywall anchor rated well above the weight. A picture hook and a nail is not enough. Hang it, then leave it alone for a day before you decide it is fine.
Leave a way to the battery
If your rim goes all the way around, the movement is in a sealed pocket and changing a battery means taking the whole clock down and off its screw. Break the rim at the bottom, or accept the annual wrestle. Once a year, so it is a real choice either way.
Bumper pads
Two small self adhesive pads on the bottom edge of the back stop the clock rocking and stop the rim scuffing paint. We keep them at the front desk on the honor system. Small thing, noticeable difference.
Fitting the movement, in order
- Rubber washer onto the shaft first, from the back. It sits between the movement and the clay and takes up any slack in a handmade hole.
- Shaft through from behind, then the brass washer and the hex nut on the front. Snug, not tight. You are threading a small brass nut against a ceramic, and the ceramic wins arguments.
- Hour hand on first. It presses onto a tapered shaft by friction rather than screwing on. Point it exactly at a number as you push it down, because you cannot twist it afterward, only lift it off and start again.
- Minute hand next, then the cap nut, then the second hand if you are using one. Set the minute hand pointing at twelve as you fit it.
- Check the hands clear each other and the face before the battery goes in. On a dished face they will, which is one of the quiet advantages of dishing it.
- Battery in, then leave it running for a day before you hang it. A movement that is going to stall on hands that are too heavy will do it in the first few hours.
Keep this open at the table
The whole thing, on one screen
Tap copy and it lands in your notes app, so you are not scrolling a page with clay on your thumb.
Before you start
- Movement bought, rated for a half inch dial
- Roll the slab at three eighths of an inch
- Compress both faces with a rib
- Slump it, do not drape it
- Aim for about twelve inches finished
While you build
- Center hole: half an inch, wet
- Never past five eighths
- Clean the burr off both sides
- Back rim three quarters of an inch tall
- Keyhole cut into the rim, not onto it
- Break the rim at the bottom for the battery
Drying and firing
- Tented in plastic for the first few days
- Then between two boards, light weight
- Flip it once a day until firm
- Check the hole with the shaft at bone dry
- Glaze the front only. No stilts
- Buy the hands after firing. Under five inches
Diagnosis
Seven things that go wrong, and why
Two things that go wrong
Find the one that just happened to you.
The shaft will not reach through
The movement was rated for a thinner dial than fired stoneware. Nothing on the pot can be changed, so buy a movement with a longer shaft, which is a ten dollar problem rather than a lost clock. Grinding the back of the piece thinner around the hole is possible with a wet diamond pad if you are only a fraction short.
The hole is too small
It was cut at three eighths or less and shrank onto the shaft. A wet diamond core bit will open it, slowly and with water running, and the odds are decent on a well fired piece. Next time cut it at half an inch and check it against the shaft at bone dry.
It came out of the kiln rocking
Warped, and the cause was almost certainly drying rather than firing. It cannot be flattened. If the rock is small, two bumper pads at the bottom will hide it on a wall. If it is large, the next one gets compressed, tented, boarded and flipped.
It cracked across the middle while drying
The floor was not compressed enough, or the center stayed wet while the rim went hard and the two shrank against each other. Compress harder next time and dry it under plastic for longer. A crack in greenware is not repairable in any way that survives cone 5½.
The hands catch on the face
Usually the nut was overtightened, pulling the shaft down, or the hands were bent in the packet. Loosen the nut a quarter turn, and gently flatten the hands against a table with a fingertip. On a domed face rather than a dished one, this is not fixable and the hands have to get shorter.
It runs slow, or stops
Almost always hands that are too long or too heavy for a standard movement. Anything over five inches wants a high torque one. Check for a hand rubbing the face or the second hand touching the minute hand, which stalls a motor just as effectively as weight does.
It hangs crooked or leans off the wall
The movement box is holding the middle off the plaster. Either the back rim is not deep enough to clear it, or the piece has no rim and is pivoting on the box. Bumper pads help a small lean. A large one is a design problem to solve on the next piece.
Bring it to somebody before you try to fix it
Main instructors are the folks in the pink tees, and there are several in the room during every instructed class. A fair number of these are recoverable if nobody has attempted a rescue yet.
House rules
What applies to a clock here
Clocks themselves have no special rules. The materials and the firing do.
- Color goes on raw clay and gets bisqued firstUnderglaze, engobe and slip all go on before the bisque, never straight into a glaze bucket. Unfired color lifts off and one piece can spoil a shared bucket. Bisque firings are free, so this costs time and nothing else.
- Two underglaze brands, one engobe brandSpeedball Underglaze and Amaco Velvet Underglaze, and Mayco for engobes. Bring your own of those at any Level. Nothing else comes through the door, because unknown chemistry in a shared kiln is how a studio loses shelves.
- Anything that might run goes on a kiln cookieA flat piece fired lying down sends a runny glaze outward toward the rim. Cookies are made from your own scrap clay, rolled like a thin tortilla, about three quarters of an inch wider than whatever sits on it.
- No dry sanding fired work, at any LevelOpening up a hole or scuffing the back for epoxy is wet work only, with a diamond pad or a wet sanding sponge. This one is not negotiable and it is not about the pot.
- Glaze fires to cone 5½Cone 5 with a twelve minute hold, so between cone 5 and cone 6. Bisque goes to cone 05. It matters here because a large flat form is the kind of piece that finds out whether a glaze is stable at that temperature.
- Firing is charged by sizeFive cents per cubic inch on the glaze firing with a four dollar eighty minimum, measured at the widest points. Bisque firings are free, every time.
Questions
The ones we get asked
Still stuck?
Ask a main instructor. They are the folks in the pink tees, and there are several in the room during every instructed class.
How big should my first one be?
Ten to twelve inches finished. Small enough that warping has little leverage and the weight stays sensible, big enough to read from across a room, and comfortably inside the five inch hand limit of a standard movement. Under about eight inches a flat slab works fine with no slab mold at all, which makes a small clock the easiest possible first attempt.
Which clay should I use?
Something with a little tooth. B-Mix w/Grog is the friendliest choice for a wide flat form, because grog resists the warping and cracking that a big slab invites. 52 Buff is fine and shrinks the least at ten percent. #16 Porcelain will give you the most beautiful face and the most warping, so save it for the second one.
Can I drill the hole after it is bisqued?
You can, with a diamond core bit and water running, and it works often enough to be a real rescue. It is not a plan. Bisque is a ceramic, it chips rather than cuts, and a chip on the front face of a clock is right where everybody looks. Cut the hole in soft clay and check it at bone dry.
Do the numbers shrink out of position?
No. Everything on the face shrinks by the same fraction at the same time, so a mark that was at twelve o’clock stays at twelve o’clock and stays the same distance from the hole in proportion. The hands are the only part of the project that does not shrink, which is the entire reason we keep saying to buy them last.
What size hands do I need?
Measure your fired clock from the center hole to wherever you want the minute hand to stop, usually just short of the hour marks. That measurement is the minute hand length, since hands are sold measured from the mounting hole to the tip. The hour hand is normally about seventy percent of it, and sets are sold matched. Under five inches for a standard movement.
Can I make a much bigger clock?
Yes, and two things change. You need a high torque movement, which drives hands up to about seventeen inches. And the weight climbs fast, because it grows with the square of the diameter, so a twenty inch clock is nearer ten pounds than four. That is a stud and a proper screw, not an anchor, and it wants a thicker wall and a deeper back rim to stay flat through the firing.
Is a slumped dish really better than a flat disc?
For anything over about eight inches, yes, and not by a small margin. A curved sheet is dramatically stiffer than a flat one, which is why corrugated roofing exists. The dish also gives the movement a hollow to sit in and the clock a rim to stand on. A flat disc is not wrong, it just asks more of your drying discipline and leaves you to solve the standoff separately.
Can I put a clock movement in something other than a disc?
Anything with a flat area of the right thickness and a hole through it will take a movement. People make clocks out of tiles, shallow bowls, slabs cut as animals, and plaques with a separate face inset. The only real constraints are that the material at the shaft has to be thin enough for the post you bought, and there has to be somewhere behind it for a box two and an eighth inches square to live.
Does a clock cost more to fire?
No. Glaze firing is five cents per cubic inch with a four dollar eighty minimum, measured at the widest points, and bisque firings are free. A flat piece is mostly air by that measure, so a twelve inch clock is one of the cheaper things you will put in a kiln this month.
Go make one
Buy the movement, then start the clay
Everything on this page comes back to one habit, and it is not a clay skill. It is deciding the hardware before you decide the design, and then letting the clay be measured against something real. Do that once and a clock stops being an intimidating project and becomes what it actually is, which is a nice flat pot with a hole in it and a very good excuse to spend three hours on a drawing.
That is enough to go and make a good one. There is a much longer version of this page behind the Comprehensive toggle at the top, with seven videos, three ways to build the face, the glazing section and the reasons behind every rule here.
Which version would you like to print?
Videos come out as a labelled box with the title and channel to search for, since paper does not play them.